1. FIELD OF THE INVENTION
This invention relates to an apparatus for measuring gears (hereinafter referred to as a gear measuring apparatus), and particularly for measuring the tooth form of large-diameter spur ring gears or helical ring gears and for detecting pitch of the gear.
2. DESCRIPTION OF THE RELATED ART
For example, a conventional gear measuring apparatus disclosed in Japanese Patent Examined Publication No. 58-7923 measures the tooth form of a gear in the following way.
With the gear supported at its upper and lower center, the rotation of the lower center with the aid of a main shaft by a worm wheel speed reducer causes the gear to rotate. A probe is attached to the tooth surface of the gear and is made to travel linearly while the gear is rotated. At this stage, the deviation between the actual tooth form and the standard involute tooth form is determined from the angle of rotation of the gear and the linear distance traveled by the probe.
An apparatus similar to the above-mentioned apparatus is capable of detecting pitch of the gear as follows:
The probe is brought into contact with a pitch point and this point is designated the zero point. The probe is withdrawn to a fixed position and the gear is rotated by only one tooth. The probe in the fixed position is moved to a measuring position to bring the probe into contact with the pitch point. The probe reading at this time indicates a pitch error. The above-described operation is sequentially performed for each tooth and pitch errors are thereby obtained. The pitch errors obtained in this manner are errors accumulated from the zero point.
In such a conventional gear measuring apparatus, however, the gear must be supported by the apparatus for measuring. As a result, the supporting structure must be large and so must the apparatus when large gears such as those of one to two m dia. are measured, thereby leading to an expensive apparatus.